As it can be seen in FIG. 7a, conventional skateboard comprises an oval plate(111) and two wheel-sets(113,123) which are mounted on the underside of the plate(111), each of the wheel-sets carries two wheels. With this configuration, the conventional skateboard can be accelerated by the rider's stamping onto the ground and it can be steered to the right or left direction by the rider's leaning to one side or the other side of the plate(111). As it can be seen in FIG. 7b, a conventional caster(130) comprises a wheel support(134), roller arm(135) and a roller(136). Such a conventional caster(130) is generally used as front wheel in a handcart because it easily changes its rolling direction by application of a minimal turning force by the user.
However, without the rider's stamping onto the ground, the conventional skateboard cannot be accelerated or can be accelerated only by an extremely skillful rider.
Besides, there is another problem that the conventional skateboard cannot be tilted much for the right or left turn because the plate(111) touches the wheel of the wheel-set when the plate(111) is tilted more than a specific angle. With this reason, the conventional skateboard can be steered to a relatively small degree, so that it is not possible to change the direction of the skateboard for making a turn within a small turning radius.
Therefore, it is needed and is the objective of this invention to provide a skateboard which is much more steerable than the conventional skateboard and which can be accelerated without the rider's stamping onto the ground.